1. Field of the Invention
The present invention relates to a packet transmission apparatus, a packet transmission system and a packet transmission method used in an apparatus having, for example, an IEEE 1394 serial interface.
2. Related Background Art
When sending out a packet, a conventional transmission apparatus first reads in a packet to be transmitted via a CPU bus by a PIO (Programmed I/O) or a DMA (Direct Memory Access) , and writes the packet into a inside storage unit such as a FIFO (First In First Out) (packet preparation operation).
If the packet preparation operation is completed, the transmission apparatus sends a transmission request onto an IEEE 1394 bus (network bus). Upon acquiring a transmission permission (transmission right) from a bus manager connected to the IEEE 1394 bus, the transmission apparatus outputs a packet stored in the storage unit onto the IEEE 1394 bus. In other words, the transmission apparatus transmits the packet to a transmission destination.
As heretofore described, the transmission apparatus starts packet transmission after the packet preparation operation is completed. When the size of the packet to be transmitted is large, therefore, it takes a long time for the above-described packet preparation operation. This results in a problem of delayed completion of data transmission.
Furthermore, if the size of the packet to be transmitted is large, the time over which the transmission apparatus continuously occupies the IEEE 1394 bus becomes long. While the transmission is being conducted, another IEEE 1394 device cannot conduct data transmission. Even if another device is to transmit a small amount of data, therefore, it must wait for transmission for a long time. As a result, transmission of a packet having a large size becomes a cause of lowering the transmission efficiency by another IEEE 1394 device.